1. Field of the Invention
This invention relates generally to a system and method for providing security for one-way message transmissions and, more particularly, to a system and method for providing security for short message system messages, where the system and method use a synchronized clock signal that is added to the message.
2. Discussion of the Related Art
Communications systems are known in the art that allow a central service center to communicate wirelessly with a vehicle to provide various services, such as unlocking the vehicle, updating the software in the various ECUs within the vehicle, etc. The central service center will include a server that allows it to wirelessly communicate with the vehicle over the designated frequencies through one or more of cellular based communications, land-lines, satellite communications and the internet.
These types of wireless communications systems sometimes employ short message system (SMS) communications links where the messages are transmitted on a one-way channel with no return transmissions. In other words, there is no verification that the message is received. These types of SMS communications links are desirable because they reduce the amount of bandwidth and power required to provide the communications link. For example, in the vehicle communications system discussed above, a vehicle operator may call the service center to ask that the vehicle doors be unlocked. The service center may wireless communicate the command to unlock the door using an SMS message at low bandwidth and low cost.
A potential security threat exists with this type of SMS communications link. Particularly, it is possible for a hacker to receive and record the transmitted message from the service center to the vehicle and/or prevent the message from the service center from reaching the vehicle. The hacker can then replay the message at a later time to perform a particular function. For example, if an SMS message is sent to unlock the vehicle doors, the hacker can block the message at the router level or in the air by jamming the signal. Because the captured message is a valid message, the hacker can replay the message at a later time when the vehicle owner is not close to the vehicle and gain unauthorized access to the vehicle.